Wooden decking structures such as those described in Applicant's earlier issued patents, namely, U.S. Pat. No. 4,622,792 and U.S. Pat. No. 5,134,813, typically are subject to harsh climatic conditions.
The two most common components of decking materials, wood planks and nails exhibit significantly different physical characteristics, particularly upon extended exposure to cyclical changes in ambient conditions. In temperate climates, during the warmer months, decks are routinely exposed to rain and direct, unfiltered sunlight. During the winter, as a result of heavy snowfalls and ice, the deck surface may be subject to multiple freeze-thaw cycles which amplify the different thermal expansion coefficients of the metal and wood.
First, the coefficients of thermal expansion of metal and wood cause different dynamics with regard to expansion and contraction. Secondly, the shape stability of wood depends on moisture content where, in contrast, ambient moisture plays little role in the shape stability of the metal fasteners, e.g., nails (disregarding oxidation/rusting). As a result of repeated thermal and moisture cycles, the differences between the wood and the metal fastener structures used to secure the wood, particularly in the case of a deck surface module, generate pronounced boundary faults which manifest themselves in ever larger, cracks, split ends, pits, or gaps in the wood itself, and particularly, between the metal nails and the wood planking. These boundary faults lead to progressive separation of nails from planking and correspondingly larger exposed surface flaws such as gaps between abutting wood planking, cracks in the wood planking, checking, split ends, exposed nail heads projecting above the planking surface, and exposed nails located in the planking gaps.
Once a gap/crack/split end is established, repeated penetration of rainwater and/or ice (a third solid possessing its unique thermal expansion properties, particularly nearing the 0.degree. C. mark) promotes and exacerbates such flaws. Water behaves differently than either the wood of the planking or the metal of the nails, and actually expands during the lower end of its liquid phase just before freezing. Thus, freeze-thaw cycles contribute to the deterioration of the wood-metal interface, and hence, the overall structure. In view of these structural aging problems, exposure such as sunlight, moisture, and thermal cycles has long been recognized as the primary cause of structural aging and deterioration. A market for rehabilitory coatings and preservatives has been well established to facilitate decking maintenance, without which, the deleterious effects of the weathering process become more pronounced.
The foregoing effects not only adversely impact on the overall appearance of the structure but also, in the aggregate, may compromise the integrity of the decking structure and create a safety problem.
As a matter of basic construction technique, decking structures and the like are typically constructed where the nails are driven through the upper, exposed surface. It is evident that it is more expedient to drive nails through that upper, exposed surface. In part, this expediency has retarded construction practices of conventional decking structures and modules.